huasheng 4 stroke performance upgrades

I recently went from 44 to 38 tooth sprocket. An my speeds an rpms have changed alot. Went from 26-29 mph cruising speeds and 4500-6500 rpms. To about 28-34 mph cruising speeds with much lower rpms. My issue is even when I start a slight increase in incline my rpms drop and speeds fall to a slow...